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Marble inaccuracy

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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how to make it more accurate.........

Rifle it
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use new ammo (darts)
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Marble inaccuracy

Unread postAuthor: VH_man » Thu Jul 12, 2007 3:58 pm

i was using my marble sniper yesterday, and i decided to do some open firing, just to see if the marbles flew straight. to my amazement, they dont. at all.

at aobut 50 feet, the marbles begen to swerve off sharply in random directions.

does anyone know how to fix this? right now im looking into rifling my copper barrel, not an easy task..............
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Unread postAuthor: robert23 » Thu Jul 12, 2007 4:08 pm

I have a baseball pitching machine that has a piece of very flexible rubber at the muzzle. It puts a spin on the ball so that the pitch is not random. You might try this so you get a more consistent spin/trajectory.
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Unread postAuthor: frankrede » Thu Jul 12, 2007 4:18 pm

add backspin?
Sounds like they are hooking, much like a golfball.
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Unread postAuthor: MrCrowley » Thu Jul 12, 2007 4:21 pm

Yeah my paintballs do that as well, but fishing sinkers don't because they're so heavy the wind doesn't effect them as much I guess.
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Unread postAuthor: noname » Thu Jul 12, 2007 4:24 pm

Rifling will not help a spherical projectile whatsoever. You should probably make a hop-up. I don't know why you have this problem, maybe because it's copper? Most of my marble guns shoot perfectly straight. You can also try getting heavier marbles, or steel ball bearings.
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Unread postAuthor: robert23 » Thu Jul 12, 2007 4:25 pm

frankrede wrote:add backspin?
Sounds like they are hooking, much like a golfball.

Actually the pitching machine that I have adds a forward spin to the ball. Either way, adding the same spin every time would provide more consistency, which you could learn to predict.
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Unread postAuthor: jrrdw » Thu Jul 12, 2007 4:27 pm

I've herd/read/gotten the idea that if you sabot a round ball, that helps. Makes me wonder how in the days of old they managed to eat, guess they built good traps.
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Unread postAuthor: Hawkeye » Thu Jul 12, 2007 4:41 pm

Noname, Do a bit more research before making a sweeping statement like that. Muskets use a round ball and they gained significantly in accuracy with the advent of rifling.
It is more correct to say that the rifling needs to bite into the projectile to put the spin on it.
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Unread postAuthor: robert23 » Thu Jul 12, 2007 4:57 pm

Hawkeye wrote: Muskets use a round ball and they gained significantly in accuracy with the advent of rifling.
It is more correct to say that the rifling needs to bite into the projectile to put the spin on it.


Which would explain why a sabot would help. It would give the rifling something to grip.
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Unread postAuthor: noname » Thu Jul 12, 2007 4:59 pm

OK, I just naturally assumed that it didn't, because I've heard it said at least a dozen times in the amount of time I've been on this forum.
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Unread postAuthor: VH_man » Thu Jul 12, 2007 5:06 pm

well, i cleaned out my barrel. it helped somewhat. im going to try to implement some kind of hop-up at the muzzle, mabet just bend a little lip down on the top. just gotta mark it so i put it in the same place every time.

i was thinking of putting it in the back like an airsoft gun, but im too lazy, and it would require me to build a breech, wich i dont have the dough for
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Unread postAuthor: al-xg » Thu Jul 12, 2007 5:17 pm

They have riffled barrels for paintball guns too, the riffling would just make the spin consistant just as does the hop up although a hop up makes the tradjectory more of an arch so it could also make the marbles go in other directions if it wasn't set up properly.

But riffling copper could be quite tricky...
Try porting the barrel, or cutting slots in the muzzle that might help although i would have though that marbles would be heavy enough.
Porting makes a huge difference with some projectiles.

If the barrel isn't tight enough around the marble that wouldn't help because it will be inacurrate and inconsistant, the wadding could help with that.
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Unread postAuthor: noname » Thu Jul 12, 2007 5:27 pm

A clean, easy way to make a hop-up would be using a hacksaw to cut a notch near the end of the barrel, in the top, then getting an O-ring that fits tightly over the barrel. Put the O-ring on the barrel and slide it down so the O-ring is in the notch, and in the top of the inside of the barrel, you can see the O-ring sticking out a tiny bit.
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Unread postAuthor: frankrede » Thu Jul 12, 2007 5:28 pm

robert23 wrote:
frankrede wrote:add backspin?
Sounds like they are hooking, much like a golfball.

Actually the pitching machine that I have adds a forward spin to the ball. Either way, adding the same spin every time would provide more consistency, which you could learn to predict.
But thats a pitching machine not a spudgun.
When a human pitcher pitches he adds backspin.
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Unread postAuthor: acoop101 » Thu Jul 12, 2007 6:47 pm

Rifling works best when the lans and groves can actually bite into the projectile. With marbles that isn't really possible. Also balls don't fly very well, that's why muskets are so inaccurate compared to modern rifles. try using steel round bar and grinding it to a point and see if it is more accurate.
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